Optimization of Y2BaCuO5 phase morphology for the growth of large bulk YBCO grains

YBCO samples were prepared using different types of precursor powders: quenched, or YBa2Cu3O7−x and Y2BaCuO5 commercial powders, with and without Pt addition. Two stoichiomctrics, corresponding to 0 and 40% molar excess of the Y2BaCuO5 phase, were adopted. The behavior of the Y2BaCuO5 phase through thermal treatments, typical of melt processes, was observed by quenching the samples at various stages. YBa2Cu3O7−x grain growth kinetics was enhanced and liquid phase losses were limited by optimizing the morphology of the Y2BaCuO5 phase in the partially melted state, with the simultaneous presence of round particles ≤1 μm and needle-like particles with very high aspect ratio. The optimized processing conditions were adopted, together with a seeding technique, to grow YBCO samples. At 77 K, a magnetic levitation force of 2.5 kg was measured for a sample with 18 mm diameter, and magnetization critical current densities over 104 A/cm2 were reached at 1 T.